The present invention relates generally to air conditioners and, more particularly, to air conditioners mounted on the roof of vehicles such as recreational vehicles.
Rooftop mounted air conditioners are commonly used on recreational vehicles to circulate cooled or conditioned air to the interior of the vehicle. These rooftop air conditioners include a compression refrigeration system comprising a compressor, condenser, evaporator and other components which are housed within an outer shroud and supported on a base pan. In a typical application, a centrifugal evaporator fan is provided in a plenum or chamber to draw warm indoor air from within the vehicle, direct it through the evaporator to cool the air, and then return the cooled air to the vehicle. The evaporator fan is mounted for rotation about a horizontal axis so that the tangentially directed fan discharge can be ducted directly downwardly into the interior of the vehicle. In a separate chamber, a centrifugal condenser fan draws outdoor air through grill openings in the shroud and pulls or blows it through the condenser to provide cooling of the refrigerant carried within the condenser coils. The evaporator and condenser fans are also variously referred to as impellers, wheels, propellers, and blowers.
In rooftop air conditioners of the type described above, a single motor is typically used to drive both the evaporator and condenser fans in order to reduce the costs and space requirements that would be associated with a second motor. As a result, the fans are typically mounted on a single drive shaft that extends horizontally from opposite ends of the motor. While horizontal rotation of the centrifugal evaporator fan is desirable because it allows the tangentially discharged air to be ducted directly downward into the vehicle, the diameter and resulting air flow capacity of both fans is limited by the available vertical spacing between the base pan and outer shroud. The desire to reduce the bulky appearance of rooftop air conditioners and allow adequate clearance under bridges, carports and other overhead obstructions generally requires that the vertical spacing be limited as much as possible. In certain types of low profile rooftop air conditioners which are in increasing demand because of their streamlined and aerodynamic appearance, the vertical spacing between the base pan and shroud may be ten inches or less. Because it would be desirable to use larger diameter fans to achieve better operating performance, a need has developed for a way to mount both the evaporator and condenser fans for rotation about a common vertical axis using a single motor so that the diameter of the fans is not limited by the vertical spacing between the base pan and shroud.
Another problem associated with conventional rooftop air conditioners is the need to separately package each air conditioner during transportation from the factory to the dealership where it is installed on the vehicle. During shipping, it would be desirable to stack two more air conditioners together to reduce the quantity of shipping materials required and to facilitate handling of the air conditioners.
In one aspect, the present invention is directed to a vehicle rooftop air conditioner comprising a base pan having one or more openings forming a return air intake and a conditioned air outlet. A compression refrigeration system comprising a compressor, evaporator and condenser are operatively coupled together and positioned on the base pan. A first enclosure forming a conditioned air flow plenum houses the evaporator which is operable for heat transfer with an indoor air stream flowing therethrough. A centrifugal fan positioned within the first enclosure is operable to draw indoor air from the return air intake, through the evaporator and then into the centrifugal fan for tangential discharge in a substantially horizontal plane. A scroll surrounding the centrifugal fan forms an air passage for receiving the air tangentially discharged from the centrifugal fan and redirecting it in a downward direction to the conditioned air outlet. A second enclosure forms an outdoor air flow plenum and houses the condenser which is operable for heat transfer with an outside air stream flowing therethrough. A second fan which is preferably an axial fan is positioned and operable to draw air through said condenser. A single motor drives the centrifugal and axial fans which are mounted on a drive shaft for rotation about a vertical axis. Notably, the fan diameters are not constrained by the height of the air conditioner and larger diameter fans can be utilized to increase the cooling performance of the air conditioner while maintaining the desired low profile. The cooling performance can also be increased as a result of using an axial fan in the condenser compartment because outdoor air inlets can be placed in three sides of the shroud, thereby allowing use of a U-shaped, rather than L-shaped, condenser. External condensate from the evaporator can also be delivered to the exhaust side of the axial fan, thereby eliminating the streaking of the vehicle roof that often results from simply dumping the condensate onto the roof.
In another aspect, the invention is directed to a method of circulating conditioned and outdoor air in the air conditioner described above. The method includes the steps of rotating, about a common vertical axis, a centrifugal fan positioned within an evaporator enclosure and an axial fan positioned in a condenser compartment; causing, as a result of said rotating of the centrifugal fan, indoor air to be drawn from said interior space through a return air inlet into said evaporator enclosure and then through an evaporator for heat exchange and cooling of said air, said cooled air then being drawn into a center opening of said centrifugal fan and then being expelled tangentially from said centrifugal fan in a substantially horizontal plane; capturing at least some of said tangentially expelled air from said centrifugal fan in a surrounding scroll and redirecting it in a downward direction into said interior space for cooling thereof, directing, as a result of said rotating the axial fan, outdoor air through a condenser located in said condenser compartment for heat exchange therewith and then exhausting said outdoor air through said shroud.